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2015-09-18: See my follow up post for the Swift 2.0 changes.

Sooner or later every developer will need to use an API with an NSErrorPointer in it.

For example when reading a file:

String(contentsOfFile: String,
       encoding: NSStringEncoding,
       error: NSErrorPointer)

It's not difficult to use, but if you are like me, the first time I raised my eyebrows, I was not expecting to use pointers in Swift. How do we do that?

Like most stuff, its really simple, once you know how:

var error: NSError?
let content = String(contentsOfFile: myPath,
                     encoding: NSUTF8StringEncoding,
                     error: &error)

It is important to define 'error' as a 'var', turns out that we cannot use pointers for variables created with 'let'. Even when you never intent to change the value. Also, do not assign a value to 'error', though you can assign 'nil' if you like (but the compiler will do it for you).

The API call will create an error for us if it needs to. After the API call, the 'error' will be non-nil if an error occurred.

For evaluation we use the error var as follows:

   // Read the file into a string
   var error: NSError?

   let content = String(contentsOfFile: path,
                        encoding: NSUTF8StringEncoding,
                        error: &error)

   if let message = error?.localizedDescription {
      return nil

   return content

Happy coding...

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